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Commit 57c841f1 authored by Marc Zyngier's avatar Marc Zyngier
Browse files

arm/arm64: KVM: Handle out-of-RAM cache maintenance as a NOP 



So far, our handling of cache maintenance by VA has been pretty
simple: Either the access is in the guest RAM and generates a S2
fault, which results in the page being mapped RW, or we go down
the io_mem_abort() path, and nuke the guest.

The first one is fine, but the second one is extremely weird.
Treating the CM as an I/O is wrong, and nothing in the ARM ARM
indicates that we should generate a fault for something that
cannot end-up in the cache anyway (even if the guest maps it,
it will keep on faulting at stage-2 for emulation).

So let's just skip this instruction, and let the guest get away
with it.

Reviewed-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
parent 402f3528

arch/arm/include/asm/kvm_emulate.h

+5 −0
Original line number Diff line number Diff line
@@ -138,6 +138,11 @@ static inline bool kvm_vcpu_dabt_iss1tw(struct kvm_vcpu *vcpu) 
	return kvm_vcpu_get_hsr(vcpu) & HSR_DABT_S1PTW;

}



static inline bool kvm_vcpu_dabt_is_cm(struct kvm_vcpu *vcpu)

{

	return !!(kvm_vcpu_get_hsr(vcpu) & HSR_DABT_CM);

}



/* Get Access Size from a data abort */

static inline int kvm_vcpu_dabt_get_as(struct kvm_vcpu *vcpu)

{

arch/arm/kvm/mmu.c

+16 −0
Original line number Diff line number Diff line
@@ -1430,6 +1430,22 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run) 
			goto out_unlock;

		}



		/*

		 * Check for a cache maintenance operation. Since we

		 * ended-up here, we know it is outside of any memory

		 * slot. But we can't find out if that is for a device,

		 * or if the guest is just being stupid. The only thing

		 * we know for sure is that this range cannot be cached.

		 *

		 * So let's assume that the guest is just being

		 * cautious, and skip the instruction.

		 */

		if (kvm_vcpu_dabt_is_cm(vcpu)) {

			kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));

			ret = 1;

			goto out_unlock;

		}



		/*

		 * The IPA is reported as [MAX:12], so we need to

		 * complement it with the bottom 12 bits from the

arch/arm64/include/asm/kvm_emulate.h

+5 −0
Original line number Diff line number Diff line
@@ -189,6 +189,11 @@ static inline bool kvm_vcpu_dabt_iss1tw(const struct kvm_vcpu *vcpu) 
	return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_S1PTW);

}



static inline bool kvm_vcpu_dabt_is_cm(const struct kvm_vcpu *vcpu)

{

	return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_CM);

}



static inline int kvm_vcpu_dabt_get_as(const struct kvm_vcpu *vcpu)

{

	return 1 << ((kvm_vcpu_get_hsr(vcpu) & ESR_ELx_SAS) >> ESR_ELx_SAS_SHIFT);